A 10 mL sample of 0.010 M HCl is diluted by adding distilled water at constant temperature - VCE - SSCE Chemistry - Question 8 - 2010 - Paper 1

When a strong acid like HCl is diluted with water, the concentration of H⁺ ions decreases because the same number of H⁺ ions is now distributed in a larger volume. According to the ion-product constant of water, which is at 25°C, we have:

$K_w = [H^+][OH^-] = 1.0 imes 10^{-14}$

As the concentration of H⁺ ions decreases, the concentration of OH⁻ ions must increase to keep the product constant at 25°C. Therefore, the correct response is:

Thus, the answer is B:

• decrease
• increase.